Complex alterations take place in the hypothalamus and pituitary of the male rat during the course of sexual maturation. At least some of these changes may be the result of alterations in testicular steroid secretions. One of the changes in pituitary function that takes place is the development of a self-priming effect of LHRH on LH secretion. In pubertal or adult rats, but not in immature males, pretreatment with small doses of LHRH results in a larger release of LH in response to a subsequent LHRH administration than does pretreatment with saline. The role of dynamic changes in testosterone and androstenedione during self-priming will be studied in immature and pubertal rats decapitated at various times during the process. Serum and pituitary concentrations of LH and serum levels of testosterone and androstenedione will be measured by radioimmunoassay. The role of other testicular steroids, as well as the effect of alterations in the level of testosterone, in the development and/or maintenance of the self-priming effect will also be examined. Individual animals will be tested for the presence of a self-priming effect after being treated with various doses of testosterone alone or in combination with 17 hydroxyprogesterone, androstenedione, dihydrotestosterone, 3Alpha androstanediol, 3Beta androstanediol and estradiol. The serum levels of 17 hydroxyprogesterone have been shown to be elevated just prior to or coincidient with the onset of sexual maturation in the male rat and to decline abruptly shortly thereafter. The possible role of this testosterone precursor in the initiation of the sexual maturation process will also be determined. The effect of premature and/or prolonged elevations in 17 hydroxyprogesterone on various aspects of the pubertal process will be investigated. Parameters to be studied include growth of the testes, seminal vescicles and prostate, maturation of the gonadotropin negative feedback systems, pituitary sensitivity to LHRH, the self-priming effect of LHRH, and possibly the sensitivity of the testes to gonadotropins. The long term goals of these studies is the description of the mechanism(s) controlling the onset of puberty in the males.